Thank you Martin for the help.I did different test by using 2p model with box 
and centered Finite volume and I found what you have mentioned.Can I also use 
higher order time method in Dumux?
Thank youHai 

     On Monday, November 24, 2014 9:54 PM, Martin 
<[email protected]> wrote:
   

   Hello Hai,
 
 as far as I know you usually look at strong convergence rates (every strongly 
convergent sequence is also weakly convergent). That means |u-u_h| -> 0 (in the 
corresponding Hilbert norm) implies strong convergence. As Christoph already 
mentioned, for the box method you get in general first order accuracy: second 
order for pressure which implies first order for velocity and first order in 
time because of backward or forward Euler method. 
 
 For the cell centered Finite Volume Scheme with Two-Point Flux Approximation 
you only achieve this rates for isotropic permeability tensors. If you want to 
achieve first order for general grids and permeability tensors you can use 
Multi-Point-Flux approximations. 
 
 Regards,
 Martin  
 
 
 On 11/24/2014 05:42 PM, Christoph Grüninger wrote:
  
 Hello Hai,
what do you mean by weak and strong convergence rate?

A student of my checked the L2 error for refined grids and time steps
with the Richards equation and the FV method. We got the expected first
order convergence.
You can find the detail in his Bachelor's thesis, but it is German
"Baccour, M.H.: Verifikationsproblem mit bekannter Lösung für die
Zwei-Phasen-Darcy-Gleichung"

Additional there was a Master's thesis by Markus Wolff, it's written in
English and might help. I haven't checked myself, Bernd told me that:
"Wolff, M.: Comparison of mathematical and numerical models for twophase
flow in porous media."

Just out of curiosity: What's your affiliation?

Bye,
Christoph

 
  
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